1. Field of the Invention
This invention relates to a generator and, more particularly, to a generator which is small-sized, lightweight, capable of developing an elevated velocity and suitably applied to aerospace equipment, unmanned flying objects or unmanned marine cruising objects, and in which the output voltage may be quickly adjusted automatically in response to load fluctuations or fluctuations in input speeds.
2. Prior Art
Typical of the arrangements of generators used for the aforementioned applications are on pages 112 to 117 of Shinko Denki Technical Report No. 114, vol, 32, No. -3, issued in 1987.
FIGS. 1 to 5 show the arrangements of a conventional generator.
First, FIG. 1 shows a first prior-art example of a brushless ac generator-rectifying circuit system which is constituted by a power generating section 9, made up of a permanent magnet rotor 1, EX rotary armature 2, rotary rectifier 3, generator main armature 4, permanent magnet armature 5, EX magnetic, field 6, main rotating magnetic field 7 of the generator and rectifier 8, and a voltage regulator 10 connected to the power generating section 9. When the permanent magnet rotor 1 is rotated, a three-phase alternating current is generated in the permanent magnet armature 5.
This three-phase alternating current is converted by a rectifier circuit 11 within the voltage regulator 10 into a direct current for direct current excitation of the EX magnetic field 6. The three-phase ac power is generated in the EX rotary armature 2 in proportion to the magnitude of the dc excitation and converted into the dc power by the rectifier 8 enclosed in the rotor for exciting the main rotating magnetic field 7 of the generator. Three phase ac power is generated in the main generator armature 4 in an amount proportionate to the dc excitation and rectified to produce a dc output.
FIG. 2 shows a second prior-art example of a permanent magnet-thyristor phase control rectifying system, which is constituted by a generator 9, made up of a permanent magnet rotor 1, an armature 5 and a thyristor 12, and a voltage regulator 10, made up of a phase angle control 13, a voltage detection circuit 14 and a filter unit 15. The ac output from the generator is rectified by thyristor 12 by controlling its phase control angle and passed through filter unit 15 to produce the voltage-controlled dc output.
FIGS. 3 to 5 show a third prior-art example of a so called Randell type ac generator-rectifying circuit system, which is constituted by a generator 9, made up of a Randell rotor 1A, a field winding 16, an armature winding 5 and a rectifier 8, and a voltage regulator 10.
The Randell type ac generator is constructed as shown in FIGS. 4 and 5, wherein a rotary shaft 22 is rotatably mounted in a casing 20 by means of a bearing 21, and the Randell rotor 1A is mounted on the rotary shaft 22.
A stator 23 for the armature winding 5 and a fixed field winding 16 provided on a fixed field core 24 are provided in the casing 20. The Randell rotor 1A is a claw-troth rotor made up of a rotor A, a rotor B and a connecting ring 26.
Thus the magnetic fluxes generated by the fixed field winding 16 flow through an air gap, rotor A (N pole side), another air gap, the stator 23, a further air gap, the rotor B(S pole side), the fixed field core 24 and a still further air gap in this order.
On the surface of the Randell rotor 1A, as viewed from the armature side of the stator 23, magnetic poles of the rotating magnetic field are generated, as in the case of the usual synchronous generator.
Voltage control may be achieved easily by controlling the current through the fixed field winding.
The above described prior-art generators suffer from the following disadvantages.
The first type device, while being devoid of brushes, is highly complicated in construction, and is difficult to manufacture.
The second type device is simple in construction as a generator. However, the phase-controlled output waveform is poor as a result of velocity fluctuations and the use of a filter unit is not effective to improve the output voltage characteristics so that it is difficult to realize output compensations against sudden load fluctuations.
The third type device is thought to satisfy the requirements fairly well and hence it is currently in popular use. As a major disadvantage, the field current needs to be obtained by, for example, an initial external power source, while self-starting is not feasible.
The device also suffers from field current losses as compared to the rotating magnet type device, while it is increased in weight.
In addition, the fixed field wiring needs to be controlled extensively against velocity or load fluctuations, while the field controller tends to be bulky.